The present invention relates to the manufacture of tubing, and more particularly, to the manufacture of tubing continuously from a sheet or web of heat fusible material, such as plastic, metal foil, or a laminate of plastic and metallic foil. In particular, the invention is directed to forming longitudinally seamed tubing which is cut into body size lengths to use in the manufacturing of collapsible tube containers such as toothpaste tubes.
Plastic tubing for making collapsible container bodies can be manufactured in a number of ways. For example, in U.S. Pat. No. 3,388,017 the collapsible container tubes are made by continuously advancing a web or sheet in the direction of its longitudinal axis, bringing the side edge of the web together to form a cylindrical tube with a seam, gripping the seam and passing the seam through a heating zone to fuse the seam together while maintaining continuous pressure on the seam, and then passing the seam through a cooling zone to solidify the seam. In such a process the tubing is advanced continuously and pressure is applied by an endless sealing band which moves with the advancing tube and applies pressure to the seam of the tube as the tube is being moved beneath heating elements.
One of the most economical ways to make collapsible plastic container bodies is to form the tubing by continuous extrusion, and this is the technique ordinarily practiced where the tube bodies are made entirely of plastic, e.g., polyethylene, polyvinyl chloride, etc. Another technique is to form the tubing from a supply of flat web stock by progressively folding the web around a forming horn or mandrel and seaming its edges together. This latter technique has particular utility and advantages in the making of container bodies of laminated construction comprising one or more plys of a thermoplastic material and one or more layers of a barrier material, such as metallic foil. This enables the use of a wide range of plastic films having special physical and chemical characteristics, and also permits greater versatility in certain of the important secondary operations of collapsible tube body manufacture. For example, preprinting of the flat body stock either on the barrier layer or on one of the plastic films enables greater versatility and selection in decorative art work and ordinarily is faster and therefore more economical than printing on a formed tubular body.
It is important in forming a tubular body that a strong seam is made to prevent the contents of the tube from leaking out through the seam or from the seam rupturing when pressure is applied to the tube. In order to achieve a strong seam it is necessary to apply pressure to the seam when the seam is being bonded by heat.